title: Partitioning of lysolipids, fatty acids and their mixtures in aqueous lipid bilayers: solute concentration/composition effects.
abstract: Distributions of lysopalmitoylphosphatidylcholine (LPPC), palmitic acid (PA) and their 1:1 mixtures between water and dipalmitoylphosphatidylcholine (DPPC) bilayer were determined using a fluorescence probe that selectively detects only the solutes in water. Water solute concentrations were obtained at each of several lipid concentrations. Dynamic Light Scattering experiments confirmed that the lipid/solute aggregates were vesicles in the concentration range investigated. Lipid concentration dependence of the solute component in water was fit to a thermodynamic model of solute distribution between two coexisting solvents. Water/bilayer partition coefficient and the free energy of transfer, for each of these solutes were determined from the fit. Main findings are: (1) Water/bilayer partition coefficient of solute is greater for 2 to 10% solute mole fraction than for 0 to 2%, signaling solute induced bilayer perturbation that increases bilayer solubility, beginning at 2% solute mole fraction. (2) Partition coefficients are in the order LPPC<PA<LPPC+PA at 37°C and LPPC+PA≤LPPC<PA at 50°C. This signifies synergism toward increased solute solubility in the bilayer-gel phase and lack of it in the bilayer-liquid phase when LPPC and PA are present together. Implications of the solute concentration/composition and bilayer phase dependences of the partition coefficients to the reported solute induced enhancements in transmembrane permeability are discussed.
authors.affiliation: Department of Physics and the Center for Supramolecular Studies, California State University Northridge, CA 91330-8268, USA.
authors.forename: Jasmeet
authors.initials: J
authors.lastname: Singh
authors.forename: Amy Jo
authors.initials: AJ
authors.lastname: Lai
authors.forename: Yasmin
authors.initials: Y
authors.lastname: Alaee
authors.forename: Radha
authors.initials: R
authors.lastname: Ranganathan
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D019308:Palmitic Acid / Q000737:chemistry*; D010539:Permeability; D010713:Phosphatidylcholines / Q000737:chemistry*; D012995:Solubility; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D019308:Palmitic Acid
keywords: Lipid bilayer; Lysopalmitoylphosphatidylcholine; Palmitic acid; Partition coefficient